Heretofore, the pivot stem for mounting a caster relative to an article it is to support, has been mounted directly in a tubular receptacle in the caster, with a metal locking ring, or the like, for securing the stem in the receptacle. Frequently, the mounting receptacle was open at the bottom so that it was possible that grease used to lubricate the pivotal stem, could escape and create problems with respect to staining surfaces over which the caster operated. The escape of the lubricant had the effect also of causing the caster mounting to run dry and thus made the article on which the caster was mounted, difficult to move about.
In other mountings of this type the stem sometimes was rigidly secured in the caster structure and the stem then had to rotate in the socket adapted to receive the stem in an article of furniture, or the like, which was undesirable inasmuch as suitable bearing surfaces were not usually provided in such sockets, or a special socket had to be provided. In some prior devices where non-metallic casters were used the caster body structure was molded directly onto the lower end of the stem and again the stem had to rotate in the mounting socket in the furniture. In other prior casters the pivot stem was retained in the mounting bore merely by frictional engagement, either directly with the walls of the bore, or through a bushing but this type of retention was not sufficiently positive under all conditions and sometimes resulted in dropping a caster. Some of the prior caster arrangements utilized a bearing that functioned both as a thrust bearing and a pivot for the caster but this subjected the arrangement to greater stresses at the mounting and sometimes resulted in a loosening up of the pivotal connection with consequent unstable operation of the caster.